Hollywood director James Cameron found little evidence of life when he descended nearly 11,000 metres to the deepest point in the world’s oceans last year. If only he had taken a microscope and looked just a few centimetres deeper.

Ronnie Glud at the University of Southern Denmark in Odense, and his colleagues, have discovered unusually high levels of microbial activity in the sediments at the site of Cameron’s dive – Challenger Deep at the bottom of the western Pacific’s Mariana Trench.

Glud’s team dispatched autonomous sensors and sample collectors into the trench to measure microbial activity in the top 20 centimetres of sediment on the sea bed. The pressure there is almost 1100 times greater than at the surface. Finding food, however, is an even greater challenge than surviving high pressures for anything calling the trench home.

Any nourishment must come in the form of detritus falling from the surface ocean, most of which is consumed by other organisms on the way down. Only 1 per cent of the organic matter generated at the surface reaches the sea floor’s abyssal plains, 3000 to 6000 metres below sea level. So what are the chances of organic matter making it even deeper, into the trenches that form when one tectonic plate ploughs beneath another?

Surprisingly, the odds seem high. Glud’s team compared sediment samples taken from Challenger Deep and a reference site on the nearby abyssal plain. The bacteria at Challenger Deep were around 10 times as abundant as those on the abyssal plain, with every cubic centimetre of sediment containing 10 million microbes. The deep microbes were also twice as active as their shallower kin.

These figures make sense, says Glud, because ocean trenches are particularly good at capturing sediment. They are broad as well as deep, with a steep slope down to the deepest point, so any sediment falling on their flanks quickly cascades down to the bottom in muddy avalanches. Although the sediment may contain no more than 1 per cent organic matter, so much of it ends up at Challenger Deep that the level of microbial activity shoots up.

“There is much more than meets the eye at the bottom of the sea,” says Hans Røy, at Aarhus University in Denmark. Last year, he studied seafloor sediments below the north Pacific gyre – an area that, unlike Challenger Deep, is almost devoid of nutrients. Remarkably, though, even here Røy found living microbes.

“With the exception of temperatures much above boiling, bacteria seem to cope with everything this planet can throw at them,” he says.

Ancient microbes have been discovered in bitter-cold brine beneath 60 feet of Antarctic ice, in permanent darkness and subzero temperatures of Antarctica’s Lake Vida, located in the northernmost of the McMurdo Dry Valleys of East Antarctica.

In the current issue of the Proceedings of the National Academy of Sciences, Nathaniel Ostrom, Michigan State University zoologist, has co-authored “Microbial Life at -13ºC in the Brine of an Ice-Sealed Antarctic Lake.” Ostrom was part of a team that discovered an ancient thriving colony, which is estimated to have been isolated for more than 2,800 years living in a brine of more than 20 percent salinity that has high concentrations of ammonia, nitrogen, sulfur and supersaturated nitrous oxide—the highest ever measured in a natural aquatic environment.”It’s an extreme environment – the thickest lake ice on the planet, and the coldest, most stable cryo-environment on Earth,” Ostrom said. “The discovery of this ecosystem gives us insight into other isolated, frozen environments on Earth, but it also gives us a potential model for life on other icy planets that harbor saline deposits and subsurface oceans, such as Jupiter’s moon Europa.”Members of the 2010 Lake Vida expedition team, Dr. Peter Doran (professor, University of Illinois, Chicago), Dr. Chris Fritsen (research professor, Desert Research Institute, Reno, Nev.) and Jay Kyne (an ice driller) use a sidewinder drill inside a secure, sterile tent on the lake’s surface to collect an ice core and brine existing in a voluminous network of channels 16 meters and more below the lake surface.

On the Earth’s surface, water fuels life. Plants use photosynthesis to derive energy. In contrast, at thermal vents at the ocean bottom, out of reach of the sun’s rays, chemical energy released by hydrothermal processes supports life. Life in Lake Vida lacks sunlight and oxygen. Its high concentrations of hydrogen gas, nitrate, nitrite and nitrous oxide likely provide the chemical energy used to support this novel and isolated microbial ecosystem. The high concentrations of hydrogen and nitrous oxide gases are likely derived from chemical reactions with the surrounding iron-rich rocks.

Consequently, it is likely that the chemical reactions between the anoxic brine and rock provide a source of energy to fuel microbial metabolism. These processes provide new insights into how life may have developed on Earth and function on other planetary bodies, Ostrom said. The research team comprised scientists from the Desert Research Institute (Reno, Nev.), the University of Illinois-Chicago, NASA, the University of Colorado, the Jet Propulsion Laboratory, Montana State University, the University of Georgia, the University of Tasmania and Indiana University.